An employee who is off sick for more than two consecutive days (in other words, 3 days or more) is required to produce a medical certificate signed by a medical practitioner or any other person who is certified to diagnose and treat patients, and who is registered with a professional council established by an Act of Parliament.
In other words, a medical certificate signed by a clinic sister or traditional healer is not acceptable (unless they are registered). If the employee does not produce the required medical certificate as above, then the employer is entitled to treat the period of absence as unpaid leave, although the employee is entitled to request that it be taken as paid annual leave.
It is unlawful for an employer to insist that an employee produce a medical certificate for an absence on a Friday, or on a Monday, or on the Friday and the Monday, or for an absence on the day before or the day after a public holiday.
That said, if an employee is absent on more than two occasions (even if only for one day) during the same eight-week period, then for any further absence, the employer is entitled to insist on a medical certificate, even if the absence is for only one day, and if it is not produced, then the employer is entitled to treat that absence as unpaid leave.